Corrosion occurs when metals are oxidized to their respective ions or insoluble salts. For example, corrosion of metallic iron involves conversion to soluble iron An a +2 or +3 oxidation state or to formation of insoluble iron oxides and hydroxides. Metal loss from the solubilization of the iron can cause the structural integrity of the system to deteriorate over time. This can cause leakage between the water system and process streams. Also, the formation of insoluble salts in the corrosion process can produce a build-up of deposits which impede heat transfer and fluid flow.
Aqueous brine solutions are commonly used as refrigeration media. However, brine solutions have a significant corrosive effect on metals. Therefore, in order to reduce the extent of corrosion when brine solutions are used as refrigeration media, corrosion inhibitors typically are added to the brine solutions.
Chromate has traditionally been an extremely widely used and effective corrosion inhibitor. During recent years, however, the use of chromate has come under increasing scrutiny due to environmental concerns. Unfortunately, phosphates, which are generally excellent corrosion inhibitors, are undesirable in this application as well since they generally lead to unacceptable levels of scale formation. Similarly, nitrites may also not be used since they change the nature of corrosion from general to localized. The localized corrosion formed in presence of nitrite can cause perforation in a relatively short time.
Two corrosion inhibitors which have been used extensively in fresh water systems are gluconate and sorbitol. They have been used as corrosion inhibitors in fresh-water systems at levels up to 100 parts per million (ppm). It has never been suggested use gluconate or sorbitol An brine systems, since brines may produce a different type of corrosion (pitting or localized corrosion) than encountered in fresh-water systems.
Therefore, it would be highly desirable to develop a new method of inhibiting corrosion in brine solution systems which is environmentally acceptable, economical, and will inhibit localized corrosion or scale formation.